The use of carbon electrodes for electrochemical sensing is known. For example, see: Richard L. McCreery, “Carbon electrodes: structural effects on electron transfer kinetics”, in “Electroanalytical Chemistry”, Ed. Allen J. Bard, Volume 17, pp 221-374, 1991, Marcel Dekker, New York. In addition, it has been proposed to reduce the size of graphite electrodes as is described in: S. Fletcher and M. D. Horne, “RAM Electrodes—An Introduction”, CSIRO Minerals, ISBN 0 642 20197, May 1995. However, we have found that carbon materials such as graphite tend to become quickly fouled when used in the harsh conditions of the oilfield. For example, under the pressures and temperatures in a hydrocarbon well, the chemicals present may absorb onto the surface of the graphite electrode.
Various configurations of diamond material have also been recently proposed as electrodes. See, Soh, Kang, Davidson, Wong, Wisitora-at, Swain and Cliffel, “CVD diamond anisotropic film as electrode for electrochemical sensing”, Elselvier Science B.V., 2003; Cvacka, Quaisorova, Park, Show, Muck and Swain, “Boron-Doped Diamond Microelectrodes for Use in Capillary Electrophoresis with Electrochemical Detection”, Analytical Chemistry, Vo. 75. No. 11, American Chemical Society, June 2003; and Shin, Sarada, Tryk, and Fujishima “Application of Diamond Microelectrodes for End-Column Electrochemical Detection in Capillary Electrophoresis”, Analytical Chemistry, Vol. 75, No. 3., American Chemical Society, February 2003. The Soh et al. article discloses the use of a diamond based electrode which is about 0.2 sq. centimeters. We have found that the signal to noise ratio is often too low with this type of design. The Cvacka et al. article discloses depositing a thin film of boron doped diamond on electrochemically sharpened platinum wires. This design suffers from relatively low signal to noise ratio, and it is believed that the geometry would be relatively fragile in many applications. The Shin et al. article discloses single boron doped diamond electrode which will generally require a large amplification circuit and will not be robust enough for certain applications, especially downhole.